Modern engines are increasingly required to be as efficient as possible, often running at very high pressures and temperatures. For example, modern diesel engines operate at fuel pressure levels of 300 MPa (approximately 43,500 psi) and higher. As a result, the valves must have extremely small guide clearances to achieve a minimum fuel return flow, or leakage, between the guide and the needle.
The predominant existing technique for guide matching is grind-matching the valve member, or needle, to fit the guide. This technique is able to set clearances of between two and four microns. However, since the amount of leakage decreases as a function of approximately the third power of the clearance value, there is an incentive to decrease the guide clearances even further.